Balancer device for internal combustion engine

ABSTRACT

A balancer device includes a housing fixed to an internal combustion engine, a roller bearing disposed in the housing, a balancer shaft rotatably supported in the housing by the roller bearing, a balancer weight integrally mounted on the balancer shaft and rotatably accommodated in an weight accommodation room of the housing, an introduction part that introduces a lubricating oil from the outside to the inside of the weight accommodation room, and a discharge part that provides communication between the inside and the outside of the weight accommodation room and discharges the lubricating oil from the inside of the weight accommodation room, wherein herein the roller bearing is arranged to face the weight accommodation room.

BACKGROUND OF THE INVENTION

The present invention relates to a balancer device for reducingsecondary vibration caused by rotation of an internal combustion engine.

Hereinafter, the terms “upper”, “lower”, “above”, “below” and the likeare used with respect to the direction of gravity; and the terms “front”and “rear” are used with respect to the orientation of a vehicle towhich an internal combustion engine with a balancer device is mounted.

Japanese Patent No. 5186424 discloses a balancer device for reducingsecondary vibration in an internal combustion engine, which includes ahousing fixed to the internal combustion engine, a roller bearingdisposed in the housing, a balancer shaft rotatably supported in thehousing by the roller bearing, a balancer weight integrally mounted onthe balancer shaft and rotatably accommodated in an weight accommodationspace of the housing and a gear fitted around the balancer shaft androtatably accommodated in a gear accommodation space of the housing. Inthis balancer device, an oil introduction hole is formed in an upperside of the gear accommodation space for introduction of oil from theinternal combustion engine into the gear accommodation space. Further,the gear accommodation space is arranged such that a lateral side of thegear accommodation space faces an axial end portion of the rollerbearing. When the gear is rotated with rotation of the balancer shaft,the oil in the gear accommodation space is agitated by external teeth ofthe gear so as to create an atmosphere of oil mist or splash in the gearaccommodation space. The roller bearing is lubricated by such oil mistor splash from the gear accommodation space.

SUMMARY OF THE INVENTION

In the above conventional balancer device, however, there is a case thatthe oil gets splashed by the external gear teeth and discharged out ofthe gear accommodation space through the oil introduction hole andthereby becomes insufficient in the gear accommodation space. There isalso a case that the oil becomes excessive in the gear accommodationspace due to the presence of no oil discharge hole. These cases lead tounsatisfactory oil lubrication of the roller bearing.

The present invention has been made in view of the foregoing technicalproblem. It is an object of the present invention to provide a balancerdevice for an internal combustion engine, which enables improvedlubrication of roller bearing(s).

According to one aspect of the present invention, there is provided abalancer device for an internal combustion engine, comprising: a housingfixed to the internal combustion engine and defining therein a weightaccommodation room; at least one roller bearing disposed in the housing;a balancer shaft rotatably supported in the housing by the at least oneroller bearing; a balancer weight integrally mounted on the balancershaft and rotatably accommodated in the weight accommodation room; anintroduction part that introduces a lubricating oil from the outside ofthe housing to the inside of the weight accommodation room; and adischarge part that provides communication between the inside and theoutside of the weight accommodation room and discharges the lubricatingoil from the inside of the weight accommodation room, wherein the atleast one roller bearing is arranged to face the weight accommodationroom.

According to another aspect of the present invention, there is provideda balancer device for an internal combustion engine, comprising: ahousing fixed to the internal combustion engine and defining therein aweight accommodation room; a roller bearing disposed in the housing; abalancer shaft rotatably supported in the housing by the roller bearing;a balancer weight integrally mounted on the balancer shaft and rotatablyaccommodated in the weight accommodation room; an introduction part thatallows free flow of a lubricating oil from the outside of the housingand introduces the lubricating oil to the roller bearing; and adischarge part that provides communication between the inside and theoutside of the weight accommodation room and discharges the lubricatingoil from the inside of the weight accommodation room.

According to still another aspect of the present invention, there isprovided a balancer device for an internal combustion engine,comprising: a housing fixed to the internal combustion engine anddefining therein a weight accommodation room; needle bearings disposedin the housing; drive—and driven-side balancer shafts rotatablysupported in the housing by the needle bearings such that the drive—sidebalancer shaft is rotated by rotation of a crankshaft of the internalcombustion engine and such that the driven-side balancer shaft isrotated by rotation of the drive-side balancer shaft; balancer weightsintegrally mounted on the drive—and driven-side balancer shafts androtatably accommodated in the weight accommodation room with one or bothend sides of the respective balancer weights being supported by theneedle bearings; an introduction part that introduces a lubricating oilto the weight accommodation room from the outside of the housing; and adischarge part that provides communication between the inside and theoutside of the weight accommodation room and discharges the lubricatingoil from the inside of the weight accommodation room, wherein the needlebearings are arranged to face the weight accommodation room.

It is possible in the present invention to achieve improved lubricationof the roller bearing(s) in the balancer device.

The other objects and features of the present invention will also becomeunderstood from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an internal combustion engine to which abalancer device according to a first embodiment of the present inventionis mounted.

FIG. 2 is a section view the balancer device according to the firstembodiment of the present invention as taken along line A-A of FIG. 1.

FIG. 3 is an exploded perspective view of the balancer device accordingto the first embodiment of the present invention.

FIG. 4 is a plan view of the balancer device according to the firstembodiment of the present invention.

FIG. 5 is a section view the balancer device according to the firstembodiment of the present invention as taken along line B-B of FIG. 4.

FIG. 6 is a section view the balancer device according to the firstembodiment of the present invention as taken along line C-C of FIG. 4.

FIG. 7 is a section view the balancer device according to the firstembodiment of the present invention as taken along line D-D of FIG. 4.

FIG. 8 is a plan view showing the positional and dimensionalrelationship of a balancer weight and an oil discharge hole in thebalancer device according to the first embodiment of the presentinvention.

FIG. 9 is a section view corresponding to FIG. 6 but showing a balancerdevice according to a second embodiment of the present invention.

FIG. 10 is a section view corresponding to FIG. 6 but showing a balancerdevice according to a third embodiment of the present invention.

FIG. 11 is a section view corresponding to FIG. 6 but showing a balancerdevice according to a fourth embodiment of the present invention.

FIG. 12 is a section view corresponding to FIG. 7 but showing a balancerdevice according to a fifth embodiment of the present invention.

FIG. 13 is a section view corresponding to FIG. 6 but showing a balancerdevice according to a sixth embodiment of the present invention.

FIG. 14 is a section view corresponding to FIG. 6 but showing a balancerdevice according to a seventh embodiment of the present invention.

FIG. 15 is a section view corresponding to FIG. 6 but showing a balancerdevice according to an eighth embodiment of the present invention.

FIG. 16 is a perspective view of an upper housing member of a balancerdevice, as viewed from its inner peripheral side, according to a ninthembodiment of the present invention.

FIG. 17 is a section view corresponding to FIG. 6 but showing thebalancer device according to the ninth embodiment of the presentinvention.

FIG. 18 is a section view of a balancer device according to a tenthembodiment of the present invention as taken along line E-E of FIG. 20.

FIG. 19 is an enlarged view showing the vicinity of a ring in thebalancer device according to the tenth embodiment of the presentinvention.

FIG. 20 is a plan view of the balancer device according to the tenthembodiment of the present invention.

FIG. 21 is a perspective view showing the vicinity of a pool in thebalancer device according to the tenth embodiment of the presentinvention.

FIG. 22 is a section view of the balancer device according to the tenthembodiment of the present invention as taken along line F-F of FIG. 20.

FIG. 23 is a section view of a balancer device according to an eleventhembodiment of the present invention.

FIG. 24 is a section view of the balancer device according to theeleventh embodiment of the present invention as taken along line G-G ofFIG. 23.

FIG. 25 is a section view of a balancer device according to amodification of the eleventh embodiment of the present invention.

FIG. 26 is a section view of a balancer device according to amodification of the tenth or eleventh embodiment of the presentinvention.

FIG. 27 is a section view of a balancer device according to a twelfthembodiment of the present invention as taken along line H-H of FIG. 29.

FIG. 28 is an enlarged view showing the vicinity of an introduction partin the balancer device according to the twelfth embodiment of thepresent invention.

FIG. 29 is a plan view of the balancer device according to the twelfthembodiment of the present invention.

FIG. 30 is a section view corresponding to FIG. 6 but showing a balancerdevice according to a thirteenth embodiment of the present invention.

FIG. 31 is a section view corresponding to FIG. 7 but showing a balancerdevice according to a fourteenth embodiment of the present invention.

DESCRIPTIONS OF THE EMBODIMENTS

The present invention will be described in detail below with referenceto the drawings, in which like parts and portions are designated by likereference numerals.

The following exemplary embodiments each refers to a balancer device 10for reducing secondary vibration caused by rotation of an internalcombustion engine 1 in a vehicle.

[First Embodiment]

As shown in FIGS. 1 and 2, the balancer device 10 is mounted to acylinder block 2 of the internal combustion engine 1.

In the internal combustion engine 1, a ladder frame 4 is fixed to alower part 2 a of the cylinder block 2 by bolts. A crankshaft 3 isrotatably supported between the ladder frame 4 and the lower part 2 a ofthe cylinder block 2 (more specifically, a shaft bearing groove of thelower part 2 a of the cylinder block 2 and a shaft bearing portion ofthe latter frame 4). An oil pan 5 is attached to an outer periphery of alower surface 4 a of the ladder frame 4 so as to store therein alubricating oil O. A large-diameter crank sprocket 6 is formed with acenter insertion hole 6 a and a plurality of external gear teeth 6 b andis fixed to a front end portion 3 a (also referred to as “support shaftportion”) of the crankshaft 3 by insertion of the support shaft portion3 a in the insertion hole 6 a. A drive pulley 7 is attached to thecrankshaft 3 at a position front of the crank sprocket 6 so as totransmit rotation of the crankshaft 3 to external equipment through atiming belt.

As shown in FIGS. 1 and 2, the balancer device 10 is arranged in a spacesurrounded by the lower surface 4 a of the ladder frame 4 and the oilpan 5. The balancer device 10 includes a housing 11 fixed to the lowersurface 4 a of the ladder frame 4 by six fixing bolts 8, a pair of driveand driven shafts 14 (as drive—and driven-side balancer shafts)rotatably supported in the housing 11 in parallel with each other alongthe front-rear direction of the internal combustion engine 1 anddrive—and driven-side thin cylindrical gears 16 and 17 press-fittedaround the drive and driven shafts 14 and 15, respectively, as shown inFIGS. 1 to 8. In the first embodiment, the drive—and driven-side gears16 and 17 are of the helical type having a plurality of external gearteeth 16 a and 17 a engaged with each other.

The housing 11 has a half-split structure of upper and lower housingmembers 12 and 13 made by aluminum die casting and vertically fastenedtogether by eight fastening bolts 9. As shown in FIG. 3, each of theupper and lower housing members 12 and 13 has a generally rectangularshape with a narrow width area and a wide width area when viewed inplan.

Frame deck portions 12 a and 13 a are formed with a predetermined widthon respective peripheral mating parts of the upper and lower housingmembers 12 and 13.

Six bolt insertion holes 12 e, 13 e are made at given outer peripheralpositions in each of the frame deck portions 12 a and 13 a for insertionof the fixing bolts 8.

First and second cross deck portions 12 b and 12 c are integrally formedon front and rear sides of the wide width area of the upper housingmember 12 so as to extend in parallel with each other across the framedeck portion 12 a in the width direction of the internal combustionengine 1. First and second cross deck portions 13 b and 13 c areintegrally formed on front and rear sides of the wide width area of thelower housing member 13 so as to extend in parallel with each otheracross the frame deck portion 13 a in the width direction of theinternal combustion engine 1.

Third cross deck portions 12 d and 13 d are formed with a shorter lengthon front sides of the narrow width areas of the upper and lower housingmembers 12 and 13 so as to extend in parallel with the first and secondcross deck portions 12 b, 13 b and 12 c, 13 c and combine with the framedeck portions 12 a and 13 a, respectively.

Eight bolt insertion holes 12 f, 13 f are made in each of the first tothird cross deck portions 12 b, 13 b, 12 c, 13 c, 12 d and 13 d forinsertion of the fastening bolts 9.

As shown in FIGS. 2 and 5 to 8, a circumferential wall 18 is formedbetween the first and second cross deck portions 12 b, 13 b and 12 c, 13c of the upper and lower housing members 12 and 13. Herein, thecircumferential wall 18 includes an upper circumferential wall 20between the first and second cross deck portions 12 b and 12 c of theupper housing member 12 and a lower circumferential wall 21 between thefirst and second cross deck portions 13 b and 13 c of the lower housingmember 13.

There is a weight accommodation room 19 defined by the first and secondcross deck portions 12 b, 13 b, 12 c, 13 c (front and rear side walls)and the circumferential wall 18 (upper and lower circumferential walls20 and 21) such that the after-mentioned drive—and driven-side counterweights 42 and 43 are rotatably accommodated in the weight accommodationroom 19. In other words, the weight accommodation room 19 is defined asa substantially cocoon-like internal space where two cylindrical spacesare adjacent to each other along the front-rear direction of theinternal combustion engine 1.

As shown in FIGS. 4 to 7, a recessed portion 22 is formed in an outercircumferential surface of an upper end region of the uppercircumferential wall 20 so as to collect therein the oil O from theinternal combustion engine 1. In the first embodiment, the recessedportion 22 is arranged at a substantially middle position of the uppercircumferential wall 20 (circumferential wall 18) in the axial directionof the shaft 14, 15 and extends in an elongated groove shape from abovethe drive shaft 14 to above the driven shaft 15.

Oil introduction holes 23 (as an introduction part) are formed in therecessed portion 22 at positions above the drive and driven shafts 14and 15 so as to provide communication between the inside and outside ofthe weight accommodation room 19 and thereby introduce therethrough theoil O from the recessed portion 22 into the weight accommodation room19.

On the other hand, oil discharge holes 24 (as a discharge part) areformed in both lateral end regions of the upper circumferential wall 20in the radial direction of the shaft 14, 15 so as to providecommunication between the inside and outside of the weight accommodationroom 19 and thereby discharge therethrough the oil O from the weightaccommodation room 19 to the oil pan 5. In the first embodiment, the oildischarge holes 24 extend almost throughout the upper circumferentialwall 20 in the axial direction of the shaft 14, 15 as shown in FIGS. 3and 7. Each of these oil discharge holes 24 is arranged at a higherposition than the surface L0 of the oil O in the oil pan 5 during stopof the internal combustion engine 1 as shown in FIG. 7.

There are also chamfered surfaces 25 formed on boundaries between aninner circumferential surface of the upper circumferential wall 20 andwall surfaces of the first and second cross deck portions 12 b and 12 csuch that, when viewed in cross section, the chamfered surfaces 25 havea substantially circular arc shape inclined gradually downwardly asshown in FIGS. 5 and 6.

Further, an oil collection groove 26 is formed in an innercircumferential surface of the lower circumferential wall 21 so as tocollect therein the oil O introduced through the oil introduction holes23 as shown in FIGS. 5 to 7. In the first embodiment, the oil collectiongroove 26 is arranged at a substantially middle position of the lowercircumferential wall 21 (circumferential wall 18) in the axial directionof the shaft 14, 15 and extends in a concave shape with a constant depthalmost throughout the lower circumferential wall 21 in the widthdirection of the internal combustion engine 1.

The oil introduction hole 23 and the oil collection groove 26 are thusarranged at substantially the same position of the weight accommodationroom 19 in the axial direction of the shaft 14, 15 as shown in FIGS. 5and 6.

As shown in FIGS. 1 and 2, a front end 14 a of the drive shaft 14protrudes from the housing 11. A balancer sprocket 27 is formed with aplurality of external gear teeth 27 a and is fixed to the front end 14 aof the drive shaft 14 by a bolt 28. A tensioner 30 is attached to afront end surface of the balancer device 10. A drive chain 29 is woundedaround the gear teeth 6 a of the crank sprocket 6 and the gear teeth 27a of the balancer sprocket 27 with the application of a tension to thedrive chain 29 by the ladder frame 4 and the tensioner 30.

When the rotation of the crankshaft 3 is transmitted to the drive shaft14 through the drive chain 29, the drive shaft 14 and the driven shaft15 are rotated in opposite directions to each other by helicalengagement of the drive—and driven-side gears 16 and 17. In the firstembodiment, the drive and driven shafts 14 and 15 are each rotated twoturns per one turn of the crankshaft 3. It is herein assumed that, inthe following explanation, the drive shaft 14 and the driven shaft 15rotate in a clockwise direction and a counterclockwise direction of FIG.1, respectively, unless otherwise noted.

As shown in FIGS. 3 and 5, first bearing grooves 31 a, 31 b, secondbearing grooves 32 a, 32 b and third bearing grooves 33 a, 33 b are madein the upper and lower housing members 12 and 13 at positions facing thefirst cross deck portions 12 b, 13 b, the second cross deck portions 12c, 13 c and the third cross deck portions 12 d, 13 d. First, second andthird cylindrical journal portions 14 b, 14 c and 14 d are formed onfront end, middle and rear end parts of the drive shaft 14 and rotatablysupported by needle bearings 34, 35 and 36 (as roller bearings) in thefirst bearing grooves 31 a, 31 b, second bearing grooves 32 a, 32 b andthird bearing grooves 33 a, 33 b, respectively.

By contrast, a rear end of the driven shaft 15 protrudes from thehousing 11 as shown in FIG. 3. An oil pump 37 is connected to the rearend of the driven shaft 15 through a width across flat part 15 a so asto suck up the oil O from the oil pan 5 by the action of rotationalforce of the driven shaft 15 and supply the oil O to respective slidingparts and drive parts of the internal combustion engine 1.

As shown in FIGS. 3 and 6, fourth bearing grooves 38 a, 38 b and fifthbearing grooves 39 a, 39 b are made in the upper and lower housingmembers 12 and 13 at positions facing the second cross deck portions 12c, 13 c and the third cross deck portions 12 d, 13 d. Fourth and fifthcylindrical journal portions 15 c and 15 d are formed on front end andmiddle parts of the driven shaft 15 and rotatably supported by needlebearings 40 and 41 (as roller bearings) in the fourth bearing grooves 38a, 38 b and the fifth bearing grooves 39 a, 39 b, respectively.

The needle bearings 35 and 40 on the first cross deck portions 12 b and13 b are arranged such that rear axial ends of the needle bearings 35and 40 face the weight accommodation room 19; whereas the needlebearings 36 and 41 on the second cross deck portions 12 c and 13 c arearranged such that front axial ends of the needle bearings 36 and 41face the weight accommodation room 19.

As shown in FIGS. 2 to 3 and 5 to 8, the drive-side counter weight 42(as a balancer weight) is integrally mounted on the part of the driveshaft 14 corresponding in position to the weight accommodation room 19(i.e., the part of the drive shaft 14 between the second and thirdjournal portions 14 c and 14 d); and the driven-side counter weight 43(as a balancer weight) is integrally mounted on the part of the drivenshaft 15 corresponding in position to the weight accommodation room 19(i.e. the part of the driven shaft 15 between the fourth and fifthjournal portions 15 c and 15 d).

As the basic structures of the drive—and driven-side counter weights 42and 43 are the same, the drive-side counter weight 42 will be mainlyexplained below.

The drive-side counter weight 42 is semi-cylindrical in shape about theaxial center of the drive shaft 14. As shown in FIGS. 3, 5 and 7, thedrive-side counter weight 42 includes, on an outer circumferentialsurface thereof, a pair of two flat surface portions 42 a located onboth sides of the axial center of the drive shaft 14 and a weightportion 42 b having a semi-circular arc cross sectional profile andprotruding from the flat surface portions 42 a toward one radialdirection of the shaft 14. In the first embodiment, the drive-sidecounter weight 42 extends substantially equally toward the front andrear in the axial direction with respect to a substantially axiallymiddle position of the weight accommodation room 19. As shown in FIG. 8,the width W1 of the drive-side counter weight 42 in the axial directionof the drive shaft 14 is set smaller than the width W2 of the oildischarge hole 24 of the weight accommodation room 19 in the axialdirection of the drive shaft 14.

A protrusion 44 of semi-circular arc cross section is integrally formedat a substantially axially middle position of the outer circumferentialsurface of the weight portion 42 b (i.e. at a position corresponding tothe oil collection groove 26 of the weight accommodation room 19) so asto protrude along the concave shape of the oil collection groove 26. Inthe first embodiment, the protrusion 44 is adjusted to a predeterminedsize such that an outer circumferential part of the protrusion 44 isplaced in the oil collection groove 26 without being in contact with aninner circumferential surface of the oil collection groove 36. In otherwords, the axial width of the protrusion 44 is set smaller than thegroove width of the oil collection groove 26; and the outer diameter ofthe protrusion 44 is set slightly smaller than the distance from theaxial center of the drive shaft 14 to the bottom of the oil collectiongroove 26. Further, the protrusion 44 extends almost throughout thecircumferential direction of the weight portion 42 b withcircumferentially opposite end surfaces 44 a of the protrusion 44 beingin flush with the flat surface portions 42 a of the drive-side counterweight 42 as shown in FIGS. 7 and 8.

Similarly, the driven-side counter weight 43 includes, on an outercircumferential surface thereof, a pair of two flat surface portions 43a located on both sides of the axial center of the driven shaft 15 and aweight portion 43 b having a semi-circular arc cross sectional profileand protruding from the flat surface portions 43 a toward one radialdirection of the shaft 15.

A protrusion 45 of semi-circular arc cross section is integrally formedat a substantially axially middle position of the outer circumferentialsurface of the weight portion 43 b with circumferentially opposite endsurfaces 45 a of the protrusion 45 being in flush with the flat surfaceportions 43 a of the driven-side counter weight 43.

The above-structured balancer device 10 operates as follows. When thecrankshaft 3 is driven and rotated upon start of the internal combustionengine 1, the rotation of the crankshaft 3 is transmitted to the driveshaft 4 through the crank sprocket 6, the drive chain 29 and thebalancer sprocket 27. Then, the drive shaft 14 is rotated at a speedtwice as fast as the rotation speed of the crankshaft 3. As the rotationof the drive shaft 14 is transmitted to the driven shaft 15 throughhelical engagement of the drive13 and driven-side gears 16 and 17, thedriven shaft 15 is rotated at the same speed in the opposite directionto the driven shaft 14. As a result, the drive13 and driven-side counterweights 42 and 43 are rotated in opposite directions to each other so asto cancel lateral centrifugal forces of the drive and driven shafts 14and 15 and generate vertical vibratory forces. The occurrence ofsecondary vibration in the internal combustion engine 1 can besuppressed by the action of such vibratory forces.

At this time, it is necessary to supply the oil O to the respectiveneedle bearings 34, 35, 36, 40 and 41 for smooth rotation of the driveand driven shafts 14 and 15.

As the supply method of the oil O, there is generally known a so-calledforcible lubrication technique to establish a lubricating oil supplypassage from the oil pump 37 to the needle bearing 34, 35, 36, 40, 41and pressure-feed the oil O by the oil pump 37 to the needle bearing 34,35, 36, 40, 41 through the lubricating oil supply passage. In thisforcible lubrication technique, however, the oil O may be suppliedexcessively to cause an increase in friction between the shaft 14, 15and the needle bearing 34, 35, 36, 40, 41 by agitation of the oil Obetween needles of the needle bearing 34, 35, 36, 40, 41 and therebyinterfere with the smooth rotation of the shaft 14, 15.

Therefore, a so-called oil mist lubrication technique is adopted forlubrication of the needle bearings 35, 36, 40 and 41, which are arrangedfacing the weight accommodation room 19, in the first embodiment. Inthis oil mist lubrication technique, the oil O in the weightaccommodation room 19 is agitated by the drive—and driven-side counterweights 42 and 43 and fed in mist or splash form to the needle bearings35, 36, 40 and 41.

The operations and effects of the first embodiment will be hereinafterdescribed with respect to the driven side of the balancer device 10 asthe operations and effects of the first embodiment are the same to bothof the drive and driven sides of the balancer device 10.

Although most of the oil O from the internal combustion engine 1 isdropped and stored in the oil pan 5, some of the oil O from the internalcombustion engine 1 is dropped into the recessed portion 22 of the upperhousing member 12 of the balancer device 10, introduced into the weightaccommodation room 19 through the oil introduction hole 23 under its ownweight and then collected in the oil collection groove 26 of the weightaccommodation room 19. When the driven-side counter weight 43 is rotatedin a state that the oil O is collected in the oil collection grove 26,the oil surface L1 of the oil O is agitated by the end surfaces 45 a ofthe protrusion 45 of the driven-side counter weight 43 (see FIG. 6) andspread in mist form or splash form. There is thus created an atmospherewhere the mist or splash of the oil O diffuses in the weightaccommodation room 19 so that the needle bearings 40 and 41 arelubricated by the mist or splash of the oil O from the weightaccommodation room 19.

By the above oil mist lubrication technique, the excessive supply of theoil O to the needle bearing 40, 41 can be prevented to decrease theresistance of the oil O caused by agitation between the needles of theneedle bearing 40, 41 and reduce the friction between the shaft 15 andthe needle bearing 40, 41. It is accordingly possible to achieveimproved lubrication of the needle bearing 40, 41 and ensure thereliability of lubrication of the needle bearing 40, 41.

Differently from the forcible lubrication technique, the oil mistlubrication technique enables lubrication of the needle bearings 40, 41without the use of the oil pump 37. It is thus possible to reduce theamount of the oil O supplied to the balancer device 10 and reduce thepower consumption of the oil pump 37 for improvement of fuel efficiency.

In the first embodiment, the driven-side counter weight 43 is adapted toperform not only the function of agitating the oil O as mentioned above,but also the function of discharging the excessive oil O from the weightaccommodation room 19 to the oil pan 5 to optimize the amount of the oilO in the weight accommodation room 19 as follows.

In the case where the oil O is present in a large amount in the weightaccommodation room 19 (e.g. the surface of the oil O in the weightaccommodation room 19 is at a high level L2 in FIG. 7), the oil O isagitated upward by a relatively wide surface area of the driven-sidecounter weight 43 (including the flat surface portions 43 a and the endsurfaces 45 a of the protrusion 45) and discharged from the weightaccommodation room 19 to the oil pan 5 through the oil discharge hole 24under the action of rotational force of the driven-side counter weight43 as shown by arrows in FIG. 7. As the axial width W2 of the oildischarge hole 24 is set larger than the axial width W1 of thedriven-side counter weight 43, the oil O can be smoothly discharged fromthe weight accommodation room 19 to the oil pan 5 through the oildischarge hole 24. It is thus possible to promptly decrease the amountof the oil O in the weight accommodation room 19 and reduce the frictionbetween the driven-side counter weight 43 and the oil O.

In the case where the oil O is present in a small amount in the weightaccommodation room 19 (e.g. the surface of the oil O in the weightaccommodation room 19 is at a low level L1 in FIG. 7), by contrast, theoil O is agitated and discharged by mainly the end surfaces 45 a of theprotrusion 45. As the amount of the oil O discharged through the oildischarge hole 24 decreases with decrease in the amount of the oil Oagitated upward by the driven-side counter weight 43, only the excessiveoil O can be discharged from the weight accommodation room 19 to the oilpan 5 through the oil discharge hole 24. It is thus possible to reducethe friction between the driven-side counter weight 43 and the oil O bylimiting the area of contact between the driven-side counter weight 43and the oil O to mainly the end surfaces 45 a of the protrusion 45.

It is less likely that the oil O will be discharged excessively andbecome insufficient for the oil mist lubrication. There can be createdthe atmosphere where the oil O diffuses in mist form or splash form inthe weight accommodation room 19 all the time for reliable lubricationof the needle bearing 40, 41.

In the case where a large amount of the oil O is constantly introducedto the weight accommodation room 19, the oil O is agitated anddischarged by the flat surface portions 43 a of the driven-side counterweight 43.

In the first embodiment, the oil collection groove 26 and the protrusion45 are arranged at the substantially middle position of the weightaccommodation room 19 in the axial direction of the shaft 14, 15 so thatthe oil O can be spread in mist or splash form from the center to bothsides of the weight accommodation room 19. It is thus possible to, eventhough the mist or splash of the oil O is generated at only one point inthe weight accommodation room 19, uniformly lubricate both of the needlebearings 40 and 41 by the mist or splash of the oil O. It is alsopossible to simplify the structure of the balancer device 10 for goodproductivity and cost reduction.

In addition, the oil collection groove 26 and the oil introduction hole23 are also arranged at substantially the same position in the axialdirection of the shaft 14, 15 so that most of the oil O introducedthrough the oil introduction hole 23 naturally flows to the oilcollection groove 26 under its own weight and can be collected in theoil collection groove 26 in the first embodiment. It is thus possible tomore efficiently generate the mist or splash of the oil O.

Furthermore, the oil introduction hole 23 is formed in the recessedportion 22 of the upper (outer) surface of the upper housing member 12in the first embodiment. It is thus possible to improve the efficiencyof introduction of the oil O into the weight installation room 19 andachieve more reliable lubrication of the needle bearing 40, 41 by themist or splash of the oil O.

Although the balancer device 10 is located inside the oil pan 5 in viewof layout design, the oil discharge hole 24 is arranged at a higherposition than the surface L0 of the oil O in the oil pan 5 during stopof the internal combustion engine 1 in the first embodiment. By thisarrangement, the oil O can be prevented from flowing backward from theoil pan 5 into the weight accommodation hole 19 through the oildischarge hole 24. It is thus possible to restrict an increase in theamount of the oil O in the weight accommodation room 19 and prevent theoccurrence of excessive friction between the oil O and the driven-sidecounter weight 43.

[Second Embodiment]

The second embodiment is basically the same as but different from thefirst embodiment in that: the inner circumferential surface of the lowercircumferential wall 21 includes tapered bottom surface areas 46inclined gradually downwardly toward the oil collection groove 26 asshown in FIG. 9. As the oil O can be guided to the oil collection groove26 by these bottom surface areas 46, it is possible to allow moreefficient diffusion of the oil O in mist or splash form for reliablelubrication of the needle bearing 40, 41.

[Third Embodiment]

The third embodiment is basically the same as but different from thefirst embodiment in that: oil collection grooves 26 are formed atpositions close to the needle bearings 40 and 41, i.e., in front andrear end regions of the weight accommodation room 19 in the axialdirection of the driven shaft 15; oil introduction holes 23 are formedat substantially the same positions as the oil collection grooves 26 inthe axial direction of the driven shaft 15; and protrusions 45 areformed on front and rear end regions of the driven-side counter weight43 so as to correspond in position to the respective oil collectiongrooves 26 as shown in FIG. 10. The generation point of the oil mist orsplash becomes close to the location of the needle bearing 40, 41 as theoil collection grooves 26 and the protrusions 45 are arranged close tothe needle bearings 40 and 41. As the oil introduction holes 23 and theoil collection grooves 26 are arranged at substantially the same axialpositions, most of the oil O introduced through the oil introductionholes 23 naturally flows to the oil collection groove 26 under its ownweight and can be collected in the oil collection grooves 26. It is thuspossible to more efficiently generate the mist or splash of the oil Oand supply the oil O to the needle bearing 40, 41.

[Fourth Embodiment]

The fourth embodiment is basically the same as but different from thethird embodiment in that that: the protrusions 45 have outercircumferential surfaces 47 inclined downwardly toward the respectiveneedle bearings 40 and 41 as shown in FIG. 11. When the oil O isagitated by the protrusions 45, the resulting mist or splash of the oilO can guided to the needle bearings 40 and 41 by these inclined outercircumferential surfaces 47 of the protrusions 45. It is thus possibleto more efficiently supply the oil O to the needle bearing 40, 41.

[Fifth Embodiment]

The fifth embodiment is basically the same as but different from thefirst embodiment in that: three concave agitation grooves 48 are formedin the outer circumferential surface of the protrusion 45 as shown inFIG. 12. In the fifth embodiment, the agitation grooves 48 arerectangular in cross section and are located at substantially equallyspaced positions in the circumferential direction of the protrusion 45.By the formation of the agitation grooves 48, the outer circumferentialsurface of the protrusion 45 becomes uneven. It is thus possible toincrease the number of contact of the outer circumferential surface ofthe protrusion 45 with the oil O in the weight accommodation room 19 andimprove the efficiency of generation of the oil mist or splash O.

Although three agitation grooves 48 are formed in the protrusion 45 inthe fifth embodiment, there is no particular limitation on the number ofagitation grooves 48 in the protrusion 45. A plurality of agitationgroove 48 can be formed in the protrusion 45.

[Sixth Embodiment]

The sixth embodiment is basically the same as but different from thefirst embodiment in that: the oil introduction holes 23 are directlymade in a flat region of the upper circumferential wall 20 without theformation of the recessed portion 22 as shown in FIG. 13. As compared tothe first embodiment where the oil O from the internal combustion engine1 is positively introduced into the weight accommodation room 19 by therecessed portion 22, the amount of introduction of the oil O into theweight accommodation room 19 becomes decreased in the sixth embodiment.In the sixth embodiment, however, the amount of introduction of the oilO into the weight accommodation room 19 can be regulated properly evenwhen a large amount of the oil O is dropped from the internal combustionengine 1. It is thus possible to suppress excessive friction between theoil O and the driven-side counter weight 43 and avoid redundant load ofthe driven-side counter weight 43 for improvement of fuel efficiency.

[Seventh Embodiment]

The seventh embodiment is basically the same as but different from thefirst embodiment in that: a protruding portion 49 is formed on the outercircumferential surface of the upper end region of the uppercircumferential wall 20 in place of the recessed portion 22; and the oilintroduction hole 23 is formed in the protruding portion 49 as shown inFIG. 14. As the protruding portion 40 interferes with the flow of theoil O from the outer (upper) circumferential surface of the uppercircumferential wall 20 to the oil introduction hole 23, the amount ofintroduction of the oil O into the weight accommodation room 19 becomessmaller in the seventh embodiment than in the sixth embodiment. It isthus possible to, even when a significantly large amount of the oil O isdropped from the internal combustion engine 1, properly regulate theamount of introduction of the oil O into the weight accommodation room19 and prevent excessive friction between the oil O and the driven-sidecounter weight 43.

[Eighth Embodiment]

The eighth embodiment is characterized as follows.

As shown in FIG. 15, the oil introduction holes 23 are formed atpositions close to the first and second cross deck portions 12 b and 12c of the upper housing member 12, i.e., close to the needle bearings 40and 41, with lower (downstream-side) opening edges 23 a of the oilintroduction holes 23 being connected to the chamfered surfaces 25 ofthe upper housing member 12.

The needle bearings 40 and 41 are arranged such that end portions of theneedle bearings 40 and 41 facing the weight accommodation room 19protrude from opposing wall surfaces 12 g and 12 h of the first andsecond cross deck portions 12 b and 12 c of the upper housing member 12toward the center of the weight accommodation wall 19 (i.e. the endportions of the needle bearings 40 and 41 facing the weightaccommodation room 19 are located closer to the center of the weightaccommodation wall 19 than the wall surfaces 12 g and 12 h of the firstand second cross deck portions 12 b and 12 c).

Further, the first and second cross deck portions 13 b and 13 c of thelower housing member 13 are arranged to protrude toward the center ofthe weight accommodation wall 19 from the end portions of the needlebearings 40 and 41 facing the weight accommodation room 19 (i.e. thefirst and second cross deck portions 13 b and 13 c of the lower housingmember 13 are located closer to the center of the weight accommodationwall 19 than the end portions of the needle bearings 40 and 41 facingthe weight accommodation room 19).

As in the case of the first to seventh embodiments, most of the oil Ointroduced through the oil introduction holes 23 flows down to the lowerside of the weight accommodation room 19 and is agitated by thedriven-side counter weight 43 for oil mist lubrication of the needlebearings 40 and 41. On the other hand, some of the oil O remains in thevicinities of the lower opening edges 23 a of the oil introduction holes23 by the action of surface tension. In the eighth embodiment, suchremaining oil O flows to the wall surfaces 12 g and 12 h of the firstand second cross deck portions 12 b and 12 c along the innercircumferential surface of the upper circumferential wall 20 as the oilintroduction holes 23 are arranged close to the wall surfaces 12 g and12 h of the first and second cross deck portions 12 b and 12 c. Inparticular, the lower opening edges 23 a of the oil introduction holes23 are connected to the chamfered surfaces 25 so as to promote the flowof the oil O to the wall surfaces 12 g and 12 h of the first and secondcross deck portions 12 b and 12 c by the smoothly inclined chamferedsurfaces 25. Then, the oil O flows down to the needle bearings 40 and 41along the wall surfaces 12 g and 12 h under its own weight andlubricates the needle bearings 40 and 41.

Namely, the above direct lubrication technique is adopted in combinationwith the oil mist lubrication technique in the eighth embodiment. Bycombination of these two lubrication techniques, it is possible to moreproperly lubricate the needle bearings 40 and 41 and further improve thereliability of lubrication of the needle bearings 40 and 41.

As the needle bearings 40 and 41 are arranged to protrude from the wallsurfaces 12 g and 12 h of the upper housing member 12 toward the centerof the weight accommodation room 19, the oil O can be easily suppliedfrom the wall surfaces 12 g and 12 h of the first and second cross deckportions 12 b and 12 c to the vicinities of the needle bearings 40 and41. In addition, it is less likely that the oil O supplied to thevicinities of the needle bearings 40 and 41 will flow down as the firstand second cross deck portions 13 b and 13 c of the lower housing member13 are arranged to protrude from the needle bearings 40 and 41 towardthe center of the weight accommodation wall 19. It is thus possible toeasily supply the oil O to the needle bearings 40 and 41 for furtherimprovement of lubrication reliability.

[Ninth Embodiment]

The ninth embodiment is basically the same as but different from theeighth embodiment in that: guide grooves 50 are formed in the wallsurfaces 12 g and 12 h of the first and second cross deck portions 12 band 12 c of the upper housing member 12 so as to provide communicationbetween the oil introduction holes 23 and the bearing grooves 38 a and39 a as shown in FIGS. 16 and 17. In the ninth embodiment, each of theguide grooves 51 has a vertically elongated shape, with one end of theguide groove 50 being in communication with the oil introduction hole 23and the other end of the guide groove 50 being in communication with thebearing groove 38 a, 39 a in which the needle bearing 40, 41 issupported. As a larger amount of the oil O can be directly supplied tothe needle bearings 40 and 41 through these guide grooves 50, it ispossible to further improve the efficiency and reliability oflubrication of the needle bearings 40 and 41.

It is herein noted that, although some of the configurations of thefirst to seventh embodiments (such as oil collection groove 26 andprotrusion 45) are eliminated from the eighth and ninth embodiments, anyof the configurations of the first to seventh embodiments can be appliedto the eighth and ninth embodiments as appropriate.

[Tenth Embodiment]

The eighth embodiment is basically the same as but different from thefirst embodiment in that two pairs of drive—and driven-side counterweights are utilized to reduce secondary vibration as shown in FIGS. 18to 22.

More specifically, parts of the housing 11 located rear of the secondcross deck portions 12 c and 13 c are enlarged. There is a second weightaccommodation room 51 defined in these enlarged parts of the housing 11.Second drive—and driven-side counter weights 52 and 53 are rotatablyaccommodated in the second weight accommodation room 51.

The second drive-side counter weight 52 is the same in shape as thefirst-mentioned drive-side counter weight 42. As shown in FIG. 18, thesecond drive-side counter weight 52 is supported in a cantilever stateby the needle bearing 36 and the journal portion 14 d of the drive shaft14. The second drive-side counter weight 52 is fixed to the drive shaft14 by a fixing bolt as shown by a two-dot chain line in FIG. 18.

Similarly, the second driven-side counter weight 53 is the same in shapeas the first-mentioned driven-side counter weight 43. As in the case ofthe second drive-side counter weight 52, the second driven-side counterweight 53 is supported in a cantilever state by the needle bearing 41and the journal portion 15 d of the driven shaft 15 and is fixed to thedriven shaft 15 by a fixing bolt.

In the tenth embodiment, the width of the cross deck portion 12 b, 13 b,12 c, 13 c, 12 d, 13 d in the axial direction of the shaft 14, 15 is setlonger than the width of the needle bearing 34, 35, 36, 40, 41 in theaxial direction of the shaft 14, 15.

As shown in FIGS. 18 and 19, rings 54 are fitted on the drive and drivenshafts 14 and 15 at positions corresponding to the first, third andfifth bearing grooves 31 a, 31 b, 33 a, 33 b, 39 a and 39 b. The rings54 are made by pressing a steel material and each includes a thincircular annular plate portion 54 a and a protruding portion 54 baxially protruding in a flange shape from an inner circumference of theannular plate portion 54 a. The outer diameter of the annular plateportion 54 a is set slightly smaller than the diameter of the bearinggroove 31 a, 31 b, 33 a, 33 b, 39 a, 39 b so that the annular plateportion 54 a is placed in the bearing grooves 31 a, 31 b, 33 a, 33 b, 39a, 39 b with a slight clearance C1 left therebetween. The innercircumference of the protruding portion 54 b is press-fitted on theouter circumference of the shaft 14, 15 such that the ring 54 rotatestogether with the shaft 14, 15. In each ring 54, a small-diameter airvent through hole 54 c is made through a connection area between theannular plate portion 54 a and the protruding portion 54 b by punchingduring the press forming.

Further, the drive-side gear 16 includes a cylindrical boss portion 16 bformed protrudingly on an end surface thereof facing the needle gear 35as shown in FIG. 18. The outer diameter of the boss portion 16 b is setslightly smaller than the inner diameter of the second bearing groove 32a, 32 b so that a distal (rear) end region of the boss portion 16 b isinserted in the second bearing grooves 32 a, 32 b with a slightclearance C2 left therebetween. A narrow air vent groove 16 c is cut inthe drive-side gear 16 from the distal end of the boss portion 16 b tothe end of the drive-side gear 16 opposite from the boss portion 16 b.Alternatively, a cut may be formed in a part of the boss portion 16 balthough not specifically shown in the drawings.

The driven-side gear 17 has the same structure as the drive-side gear 16and includes a boss portion 17 b and a narrow air vent groove 17 c.

As shown in FIGS. 20 and 21, four pools 56 are formed in the upper(outer) surface of the upper housing member 20 to store the oil O fromthe internal combustion engine 1. The pools 56 are made by depressinggiven regions of the upper (outer) surface of the upper housing member20 and are located above the needle bearings 34, 35, 36, 40, 41 so asto, when viewed from above, partially overlap the needle bearings 34,35, 36, 40, 41.

In the tenth embodiment, five introduction parts are formed in thebottoms of the pools 56 for direct introduction of the oil O from thepools 56 to the needle bearings 34, 35, 36, 40, 41. As shown in FIGS. 18and 22, each of the introduction parts includes an oil introduction hole57 and an oil reservoir 58. The oil introduction hole 57 is opened at anupper side of the upper housing member 12 and is connected at an upperend thereof to the pool 56. The oil reservoir 58 is defined as acircular annular space by the shaft 14, 15 and the bearing grooves 31 a,31 b, 32 a, 32 b, 33 a, 33 d, 38 a, 38 b, 39 a, 39 b and is connected toa lower end of the oil introduction hole 57.

As shown in FIGS. 21 and 22, one of the oil introduction holes 57corresponding to the needle bearing 41 (hereinafter also referred to as“oil introduction hole 57 a”) is integrally formed during the diecasting of the upper housing member 12 such that the oil introductionhole 57 a has an elongated hole shape to introduce a relatively largeamount of the oil O into the oil reservoir 58. By the formation of suchan elongated oil introduction hole 57 a, the air accumulated in the oilreservoir 58 can be separated and floated up to supply the clean oil tothe needle bearing 41. The other four oil introduction holes 57 areformed into a substantially circular cross-section shape by drilling.The oil introduction hole 57 a may alternatively be formed into asubstantially circular cross-section shape in the same manner as theother oil introduction holes 57.

Moreover, cylindrical weir portions 59 are formed around upstreamopening ends of the oil introduction holes 57 as specifically shown inFIG. 20. Each of the weir portions 59 is in the form of a protrusionwall protruding from the bottom surface of the pool 56 and surroundingthe oil introduction hole 57, with a part of the weir portion 59 beingopened, so as to regulate the amount of introduction of the oil O intothe oil reservoir 58.

Three of the oil reservoirs 58 corresponding to the needle bearings 34,36 and 41 (hereinafter also referred to as “oil reservoirs 58 a”) areeach closed at one end by the ring 54 and brought into communication atthe other end with the needle bearing 34, 36, 41. The other two oilreservoirs 58 corresponding to the needle bearings 35 and 40(hereinafter also referred to as “oil reservoirs 58 b”) are each closedat one end by the boss portion 16 b, 17 b of the gear 16, 17 and broughtinto communication at the other end with the needle bearing 35, 40.

Consequently, the oil O is dropped from the internal combustion engine 1into the pools 56 and introduced into the oil reservoirs 58 through theoil introduction holes 57. At this time, the amount of the oil Ointroduced into the oil reservoirs 58 is regulated and optimized asappropriate by the oil introduction holes 57 and the weirs 59. The oil Ointroduced into the oil reservoirs 58 can be properly and directlysupplied to the needle hearings 34, 35, 36, 40, 41 by free flow as theoil reservoirs 58 arc arranged facing the axial ends of the needlebearings 34, 35, 36, 40, 41. It is thus possible to improve thereliability of lubrication of the needle bearing 34, 35, 36, 40, 41.

As the air in the oil O can be separated and reduced by once storing theoil O in the wide pool 56, it is possible to supply the deaerated cleanoil O and smoothly lubricate the needle bearing 34, 35, 36, 40, 41 forimprovement of lubrication reliability.

In the tenth embodiment, the oil reservoir 58 a is defined by the ring54 in which the air vent through hole 54 c is formed; whereas the oilreservoir 58 b is defined by the gear 16, 17 in which the air ventgroove 16 c, 17 c is formed. By this air vent system, the air in the oilO can be discharged from the oil reservoir 58 through the air ventthrough hole 54 c or the air vent groove 16 c, 17 c. It is thus possibleto achieve the more reliable supply of the oil O to the needle bearing34, 35, 36, 40, 41 for improvement of lubrication reliability.

Furthermore, the clearance C1, C2 is formed on a side of the oilreservoir 58 opposite from the needle bearing 34, 35, 36, 40, 41 sothat, even when the oil O reaches a high temperature under the influenceof frictional heat caused by operation of the needle bearing 34, 35, 36,40, 41, the high-temperature oil O can be discharged to the outside ofthe oil reservoir 58 through the clearance C1, C2. It is thus possibleto prevent the needle bearing 34, 35, 36, 40, 41 from becoming high intemperature and improve the durability and reliability of the needlebearing 34, 35, 36, 40, 41.

It is further possible to reduce component count for reduction ofmanufacturing/assembling cost as the oil reservoir 58 is defined by theboss portion 16 b, 17 b of the gear 16, 17.

Although the oil reservoir 58 b is defined by insertion of the bossportion 16 b, 17 b of the gear 16, 17 in the bearing grooves 32 a, 32 b,38 a, 38 b in the tenth embodiment, it is alternatively feasible todefine the oil reservoir 58 b by setting the outer diameter of the bossportion 16 b, 17 b larger than the inner diameter of the bearing grooves32 a, 32 b, 38 a, 38 b and placing an end surface of the boss portion 16b, 17 b in face-to-face arrangement with an end surface of the secondcross deck portion 12 b, 13 b.

[Eleventh Embodiment]

The eleventh embodiment is basically the same as but different from thetenth embodiment in that: one pair of drive—and driven-side counterweights are utilized to reduce secondary vibration as in the case of thefirst embodiment; and thin disc-shaped flange walls 60 are formed onboth axial end regions of the drive—and driven counter weights 42 and 43as shown in FIGS. 23 and 24. The outer diameter of the flange wall 60 isset slightly smaller than the inner diameter of the bearing groove 32 a,32 b, 33 a, 33 b, 38 a, 38 b, 39 a, 39 b so that the flange wall 60 isinserted in the bearing grooves 32 a, 32 b, 33 a, 33 b, 38 a, 38 b, 39a, 39 b with a slight clearance C3 left therebetween as shown in FIG.24. As shown in FIG. 23, one axial ends of the oil reservoirs 58adjacent to the weight accommodation room 19 are closed by the flangewalls 60. Air vent grooves 60 a are cut in the flange walls 60 atpositions different from the positions of the counter weights 42 and 43.

As mentioned above, the flange walls 60 of the counter weights 42 and 43are utilized as the partitions of the oil reservoirs 58 in the eleventhembodiment. It is thus possible in the eleventh embodiment to obtain thesame effects as in the tenth embodiment and, at the same time, reducecomponent count for reduction of manufacturing/assembling cost.

Although one axial end of the oil reservoir 58 is closed by insertion ofthe flange wall 60 into the bearing grooves 32 a, 32 b, 33 a, 33 b, 38a, 38 b, 39 a, 39 b in the eleventh embodiment, it is alternativelyfeasible to close one axial end of the oil reservoir 58 by setting theouter diameter of the flange wall 60 larger than the inner diameter ofthe bearing grooves 32 a, 32 b, 33 a, 33 b, 38 a, 38 b, 39 a, 39 b andplacing the flange wall 60 in face-to-face arrangement with the bearinggrooves 32 a, 32 b, 33 a, 33 b, 38 a, 38 b, 39 a, 39 b as shown in FIG.25. In this case, the high-temperature oil O can be discharged to theoutside of the oil reservoir 58 through a clearance C4 between theface-to-face arrangement regions.

The configuration of the eleventh embodiment (i.e. the partitioning ofthe oil reservoir 58 by a portion of the counter weight) is applicableto the case where the counter weight is supported in a cantilever stateas in the tenth embodiment.

It is also alternatively feasible to form the housing 11 as a so-calledintegrated housing without being divided into upper and lower housingmembers as shown in FIG. 26 although the housing 11 is constituted bythe upper and lower housing members 12 and 13 in the tenth and eleventhembodiments.

[Twelfth Embodiment]

The twelfth embodiment is basically the same as but different from theeleventh embodiment in that: one introduction part (oil introductionhole 57 and oil reservoir 58) is provided for each of the drive anddriven sides of the balancer device 10, rather than for each of theneedle bearings 34, 35, 36, 40 and 41, as shown in FIGS. 27 to 29.

Hereinafter, the drive-side introduction part mainly explained below asthe basic structure of the drive-side introduction part is the same asthat of the driven-side introduction part.

As shown in FIG. 27, the introduction part includes, in addition to theoil introduction hole 57 and the oil reservoir 58, an oil supply path 61arranged in communication with the oil reservoir 58 to directly supplythe oil O from the oil reservoir 58 to the needle bearings 34, 35 and36. The oil supply path 61 includes a main oil passage 61 a extendingthrough the axis of the drive shaft 14 and branch oil passages 61 b, 61c and 61 d extending radially outwardly from the main oil passage 61 aand communicating with the inner circumferential surfaces of the needlebearings 34, 35 and 36.

By this oil introduction part, the oil O can be reliably supplied fromthe branch oil passage 61 b, 61 c, 61 d to the needle bearing 34, 35, 36under the pumping action caused due to centrifugal force by rotation ofthe drive shaft 14. It is thus possible to increase cooling performanceby sufficient lubrication of the needle bearing 34, 35, 36 and improvethe durability and reliability of the needle bearing 34, 35, 36.

In the twelfth embodiment, the flow passage area of the rear-side(downstream-side) branch oil passage 61 d is set larger than that of themiddle branch oil passage 61 c; and the flow passage area of the middlebranch oil passage 61 c is set larger than that of the front-side(upstream-side) branch oil passage 61 b. It is thus possible touniformize the amount of introduction of the oil O to the needlebearings 34, 35 and 36.

Further, there is a slight clearance C5 left between the oil reservoir58 and the drive shaft 14 such that the oil reservoir 58 is incommunication with a drain hole 62 of the lower housing member 3 throughthe clearance C5 as shown in FIG. 28. The drain hole 62 is incommunication with the outside of the housing 11 so that the air,impurities or contaminants in the oil O can be discharged from the oilreservoir 58 to the outside through the drain hole 62.

As the oil O is supplied to a plurality of needle bearings by oneintroduction part, it is necessary to collect and introduce a largeamount of the oil O from the internal combustion engine 1 to theintroduction part. For this reason, an oil collection rib 65 is formedon the rear end region of the upper surface of the upper housing member12 so as to increase the amount of collection of the oil O as shown inFIG. 29.

As mentioned above, it is possible to improve the reliability oflubrication of the needle bearing 34, 35, 36, 40, 41 as the oil O can bedirectly supplied to the needle bearing 34, 35, 36, 40, 41 even in thetwelfth embodiment.

It is alternatively feasible in the twelfth embodiment to use slidebearings such as plain bearings in place of the needle bearings 34, 35,36, 40 and 41.

[Thirteenth Embodiment]

The thirteenth embodiment is basically the same as but different fromthe first embodiment in that: a mesh type oil filter 64 (as filtermembers) is arranged in the oil introduction hole 23 as shown in FIG.30. Although not specifically shown in the drawing, the oil filter 64 isprovided to each of the drive—and driven-side introduction holes 23. Asa foreign substance (such as impurities or contaminants) can be filteredout and removed from the oil O by the oil filters 64 at the time ofintroduction of the oil O to the weight accommodation room 19, it ispossible to prevent the entry of the foreign substance into the needlebearing 34, 35, 36, 40, 41 and improve the durability of the needlebearing 34, 35, 36, 40, 41.

[Fourteenth Embodiment]

The fourteenth embodiment is basically the same as but different fromthe first embodiment in that: the drive shaft 14 and the driven shaft 15are rotated in opposite directions to those of the first embodiment asshown by arrows in FIG. 31. Namely, the oil O is agitated in oppositedirections by the drive—and driven-side counter weights 42 and 43 andforced upward under the action of rotational force of these counterweights 42 and 43.

In consideration of such oil flow, interference wall portions 65 areformed on respective lateral edges of the upper circumferential wall 20as shown in FIG. 31. In the fourteenth embodiment, the interference wallportions 65 are arranged so as to extend substantially linearly from thelateral edges of the upper circumferential wall 20 and cover the uppersides of the oil discharge holes 24. Further, the interference wallportions 65 have, on lower sides thereof, guide surfaces 66 formed in asubstantially circular arc cross-section shape throughout the front-reardirection and inclined downwardly toward the oil discharge holes 24.

When the oil O is agitated and forced upward by the rotation of thecounter weight 42, 43, the guide surface 66 of the interference wallportion 65 interferes with the upward flow of the oil O, change thedirection of the flow of the oil O in a folded manner and guides theflow of the oil O toward the oil discharge hole 24 so that the oil O canbe efficiently and effectively discharged to the oil pan 5 through theoil discharge hole 24. The discharge part attains substantially the sameoil discharge performance even when the drive and driven shafts 14 and15 are rotated in opposite directions to those of the first embodiment.It is thus possible to properly decrease the amount of the oil O in theweight accommodation room 19 and reduce the friction between the counterweight 42, 43 and the oil O.

The configurations of the thirteenth and fourteenth embodiments can beapplied to not only the oil mist lubrication type but also the directlubrication type.

[Other Embodiments]

In the above embodiments, the balancer device 10 is mounted to the lowerpart 2 a of the cylinder block 2 of the internal combustion engine 1through the ladder frame 4. It is alternatively feasible to mount thebalancer device 10 directly to the lower part 2 a of the cylinder block2 of the internal combustion engine 1 in the case where no ladder frame4 is provided.

In the above embodiments, the oil O dropped from the internal combustionengine 1 is introduced to the needle bearing 34, 35, 36, 40, 41 by theintroduction part. Alternatively, the oil O from the oil pump 37 may beintroduced to the needle bearing 34, 35, 36, 40, 41 by the introductionpart upon connection of the oil pump 37 to the introduction part. Inthis case, it becomes easier to control the amount of introduction ofthe oil O to the needle bearing 34, 35, 36, 40, 41. It is also possibleto supply the oil O from which impurities or contaminants have beenfiltered out to the needle bearing 34, 35, 36, 40, 41 and improve thedurability of the needle bearing 34, 35, 36, 40, 41.

The present invention is based on Japanese Patent Application No.2014-228519 (filed on Nov. 11, 2014) of which the entire contents areherein incorporated by reference.

Although the present invention has been described with reference to theabove exemplary embodiments, it will be understood that the presentinvention is not limited to these exemplary embodiments. Various changesand modifications of the embodiments described above will occur to thoseskilled in the art in light of the above teachings. The scope of thepresent invention is defined with reference to the following claims.

What is claimed is:
 1. A balancer device for an internal combustionengine, comprising: a housing fixed to the internal combustion engineand defining therein a weight accommodation room; at least one rollerbearing disposed in the housing; a balancer shaft rotatably supported inthe housing by the at least one roller bearing; a balancer weightintegrally mounted on the balancer shaft and rotatably accommodated inthe weight accommodation room; an introduction part that introduces alubricating oil from an outside of the housing to an inside of theweight accommodation room; and a discharge part that providescommunication between the inside and an outside of the weightaccommodation room and discharges the lubricating oil from the inside ofthe weight accommodation room, wherein the at least one roller bearingis arranged to face the weight accommodation room, wherein the housingincludes a pair of front and rear side walls extending in a widthdirection of the internal combustion engine and a circumferential wallformed between the side walls such that the weight accommodation room isdefined by the side walls and the circumferential wall, wherein thehousing has a collection groove formed in an inner circumferentialsurface of a lower side of the circumferential wall with respect to adirection of gravity so as to collect the lubricating oil in thecollection groove, and wherein the balancer weight has a protrusionformed thereon in a rotation direction of the balancer weight along thecollection groove.
 2. The balancer device according to claim 1, whereinthe introduction part provides communication between the inside and theoutside of the weight accommodation room.
 3. The balancer deviceaccording to claim 2, wherein the introduction part has an introductionhole opened at an upper side of the circumferential wall, and whereinthe discharge part has a discharge hole opened at a lateral side of thecircumferential wall along an axial direction of the balancer shaft. 4.The balancer device according to claim 3, wherein the at least oneroller bearing includes roller bearings disposed in the respective sidewalls of the housing, and wherein the introduction part has introductionholes formed in regions of the circumferential wall within the vicinityof the respective roller bearings.
 5. The balancer device according toclaim 4, wherein the housing has chamfered surfaces formed on boundariesbetween an inner circumferential surface of the upper side of thecircumferential wall and wall surfaces of the side walls, the chamferedsurfaces being inclined downwardly toward the side walls, and whereinlower opening edges of the introduction holes are connected to thechamfered surfaces.
 6. The balancer device according to claim 3, whereinthe internal combustion engine has an oil pan that stores therein thelubricating oil to circulate to the internal combustion engine, andwherein the housing is located inside the oil pan.
 7. The balancerdevice according to claim 6, wherein the introduction hole is arrangedat a higher position than an oil surface of the lubricating oil in theoil pan.
 8. The balancer device according to claim 1, wherein the innercircumferential surface of the lower side of the circumferential wallincludes a surface area inclined downwardly toward the collectiongroove.
 9. The balancer device according to claim 8, wherein the atleast one roller bearing includes roller bearings disposed in therespective side walls of the housing, wherein the collection groove isarranged at a substantially middle position of the weight accommodationroom in the axial direction of the balancer shaft.
 10. The balancerdevice according to claim 9, wherein the introduction hole and thecollection groove are arranged at the same position of the weightaccommodation room or within the vicinity of each other in the axialdirection of the balancer shaft.
 11. The balancer device according toclaim 1 wherein the collection groove is formed in a region of thecircumferential wall within the vicinity of the at least one rollerbearing.
 12. The balancer device according to claim 11, wherein theprotrusion has an outer circumferential surface inclined downwardlytoward the at least one roller bearing.
 13. The balancer deviceaccording to claim 1, wherein the protrusion has a concave groove formedin an outer circumferential surface thereof.
 14. The balancer deviceaccording to claim 1, further comprising: a filter member disposed inthe introduction part so as to remove a foreign substance from thelubricating oil.
 15. A balancer device for an internal combustionengine, comprising: a housing fixed to the internal combustion engineand defining therein a weight accommodation room; a roller bearingdisposed in the housing; a balancer shaft rotatably supported in thehousing by the roller bearing; a balancer weight integrally mounted onthe balancer shaft and rotatably accommodated in the weightaccommodation room; an introduction part having a main oil passageformed in the balancer shaft and extending along a longitudinal axis ofthe balancer shaft, and a branch oil passage formed in the balancershaft and branched off from the main oil passage with respect to thelongitudinal axis of the balancer shaft, such that the introduction partallows free flow of a lubricating oil from an outside of the housing andintroduces the lubricating oil to the roller bearing via the main oilpassage and the branch oil passage; and a discharge part that providescommunication between an inside and an outside of the weightaccommodation room and discharges the lubricating oil from the inside ofthe weight accommodation room.
 16. The balancer device according toclaim 15, wherein the introduction part has a reservoir being incommunication with an axial end portion of the roller bearing so as tostore therein the lubricating oil for introduction to the rollerbearing.
 17. The balancer device according to claim 16, wherein theintroduction part has an introduction hole opened at an upper side ofthe housing and being in communication with the reservoir; and wherein aclearance on a side of the reservoir opposite from the roller bearing isarranged such that part of the lubricating oil stored in the reservoiris discharged out through the clearance.
 18. A balancer device for aninternal combustion engine, comprising: a housing fixed to the internalcombustion engine and defining therein a weight accommodation room;needle bearings disposed in the housing; drive- and driven-side balancershafts rotatably supported in the housing by the needle bearings suchthat the drive-side balancer shaft is rotated by rotation of acrankshaft of the internal combustion engine and such that thedriven-side balancer shaft is rotated by rotation of the drive-sidebalancer shaft; balancer weights integrally mounted on the drive- anddriven-side balancer shafts and rotatably accommodated in the weightaccommodation room with one or both end sides of the balancer weightsbeing supported by the needle bearings; an introduction part thatintroduces a lubricating oil to the weight accommodation room from anoutside of the housing; and a discharge part that provides communicationbetween an inside and an outside of the weight accommodation room anddischarges the lubricating oil from the inside of the weightaccommodation room, wherein the needle bearings are arranged to face theweight accommodation room wherein the housing includes a pair of frontand rear side walls extending in a width direction of the internalcombustion engine and a circumferential wall formed between the sidewalls such that the weight accommodation room is defined by the sidewalls and the circumferential wall, wherein the housing has a collectiongroove formed in an inner circumferential surface of a lower side of thecircumferential wall with respect to a direction of gravity so as tocollect the lubricating oil in the collection groove, and wherein thebalancer weight has a protrusion formed thereon in a rotation directionof the balancer weight along the collection groove.